1. Field of the Invention
This invention relates to articulated fluid transferring apparatus, and more particularly to means for controlling the position of marine loading arms and for moving the outer end of such an arm into a predetermined spatial position with respect to a tanker moored adjacent a loading station.
2. Description of the Prior Art
Fluid loading arms constructed of articulated pipe are extensively used in the petroleum industry for transferring oil or other fluids between a jetty, wharf or other loading station and a marine tanker moored alongside. Such an arm generally comprises an inboard boom or limb supported on a vertical riser pipe by pipe swivel joints to facilitate pivotal movement about horizontal and vertical axes, and an outboard boom or limb connected by a pipe swivel joint to the inboard limb so as to be pivotal relative thereto about a horizontal axis. The outer end of the outboard limb is adapted to be connected to a pipe manifold on a tanker located within reach of the arm, such as by a remotely-controllable coupler device.
When it is desired to connect the outer end of the outboard limb to the pipe manifold on the tanker moored alongside the loading station, the movement of a prior art loading arm is controlled by shore-based personnel until the outer end of the arm is located above the tanker's rail. The outer end of the loading arm must be maneuvered over the tanker rail and into position adjacent the tanker manifold without colliding with the tanker rail or any other object which could cause sparks and produce a disastrous explosion. This is difficult to do when the person controlling the movement of the loading arm is on the loading station at a considerable distance from the tanker. When the loading arm is within reach of personnel aboard the tanker, a set of control lines is plugged into a socket mounted on the outer portion of the arm, and personnel aboard the tanker then assume control of the arm to move the outer end of the arm into fluid-tight engagement with a tanker manifold. Fluid can then be transferred between the tanker and the loading station.
When an articulated loading arm installation of this type is being designed, minimum requirements are set for the reach of the arm. These requirements are expressed in terms of the horizontal displacement of the tanker parallel to and away from the jetty relative to a datum position, the maximum displacement away from the jetty due to variations in distance between the tanker manifold and the tanker rail, and the maximum vertical displacement due to variations in the water level and the height of the tanker manifold relative to the water level. These displacements define a three-dimensional space that is rectangular in section when viewed in plan or elevation, either parallel to or perpendicular to the jetty, and the space is known as the arm's "operating envelope". The arm must be able to accommodate all of these displacements so that a safe and secure connection to the tanker's manifold can be established and maintained within the limits of this envelope.
A system for sensing the spatial position of the outer end of an articulated loading arm, and for insuring that the outer end does not move outside the safe operating envelope, is described in the U.S. Pat. No. 4,084,247 issued to Peter Ball and assigned to the assignee of the present invention. However, the apparatus described in that patent does not include either means for determining the location of a tanker manifold relative to the arm limbs, or means for moving the outer end of the arm into position adjacent the tanker manifold.